When Scott Brown quit Celtic he left with the moniker. Captain. Leader. Legend.

Everybody wondered who was going to step forward and fill the role vacated by the force of nature that was Brown. Unassuming Celtic midfielder Callum McGregor donned the armband. He had learned from one of the best and then some. Eyebrows were raised at his captain credentials McGregor just got on with the job.

If you want to know what a 'Captain, Leader, Legend' is, then look no further than Sunday's game against Rangers. Celtic's £1 million transfer day deadline signing from Dundee Luke McCowan came on to make his debut in a Glasgow Derby. The 26-year-old was fulfilling his boyhood dream of playing for his idols. There would have been nerves no doubt about that. However, it is what McGregor said to McCowan that marks the 31-year-old out as someone special.

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McGregor said: "I just said to him, 'Go and play', you've got massive quality, just go and run about. I'll be with you. So let's just go."

Four words - "I'll be with you." What a comfort that must have been to McCowan. There was no hyperbole despite the occasion. McCowan walked onto that hallowed Parkhead turf with all the big expectations and big pressure removed from his shoulders. It's largely why he looked excellent in the cameo role. McGregor had relieved him of any pressure. There were no last-minute complicated details. There were no overloads of information. The Glasgow Derby deconstructed: "Go and play. You've got quality. Just go and run about."

That ladies and gentlemen in a nutshell is leadership. What a wonderful choice of words to speak to lifelong Celtic supporter McCowan who would have been desperate to make his mark and what a way to control his emotions and excitement. It was as heartwarming as it gets to say the least Delivered matter-of-factly. A bit like McGregor. He turns up in Glasgow Derbies. It is routine. It is a matter of fact.

When all else fails: "I'll be with you."

That's inspirational leadership that is. Yours truly would have run through a brick wall for McGregor after that speech. There is a reason why McGregor is the beating heart of this Celtic team. There is a reason why he is Brendan Rodgers's most trusted lieutenant on the field. He is a great captain. He is a great leader. He is a Celtic legend. Who is going to fill McGregor's shoes when he leaves?

Celtic will find that a more arduous task than replacing Brown. Celtic have been privileged to have two captains who have excelled in the role in vastly different ways but produced similar outcomes which is total domination of the Scottish football landscape.

For a while though McGregor has been technically superior in every element of his game. He is an exceptional player. He's been on a different football level to most or nearly all of his peers. He is vital to how Celitic functions, particularly in Rodgers's team. He is the fulcrum of the green and white machine. He makes Celtic tick. He controls the tempo and the style of play. He is the calm head and influence in the team. He has talent beyond belief. He has an uncanny knack for controlling the derby narrative. Just ask all the Rangers players who have failed to get near him in this fixture. It doesn't happen by accident.

This season for example Matt O'Riley has already flown the nest for £30 million to Brighton & Hove Albion. O'Riley was responsible for 37 goal contributions (19 goals and 18 assists from last season) and the Celtic supporters were asking who was going to step up to the plate this season. McGregor, that's who!

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How Scotland boss Steve Clarke must wish that McGregor had delayed his international retirement a bit longer. This season alone McGregor has produced three outstanding goals in three successive Premiership matches - a career first incidentally - and every one of them a contender for goal of the season. Who was the first player to celebrate with McGregor when he scored the third during Sunday's rout of Rangers? Paulo Bernardo.

What's all the more remarkable is that Bernardo was sitting on the bench at the time having been substituted himself and he sprinted fully 40 yards from the technical area to lift his skipper shoulder high and to let him get the acclaim he deserved for another stunning strike! That was a joyous moment in sport. Even McGregor and Rodgers shared a moment with clenched-fisted salutes knowing that the job had been well and truly done and done well. The Celtic fans know they are in good hands. McGregor is a rare breed. He is a born winner. He is a leader of men. A one-club man.

(Image: Ross MacDonald SNS Group)

As Rodgers said: "Celtic won't be the end game for some of these players, but it's going to give them so much. When you leave here you are a winner, a better footballer and ready to play for any team in the world. It's the model of the club. Callum (McGregor), James (Forrest) these guys, they love being here; they’ve had opportunities to move, but have stayed happy in Scotland. They’re happy playing for Celtic and happy winning trophies.

"For other players that maybe are outside of that, it's different, but that's OK. We have to accept that. There's an opportunity here. The experience that you can gain on and off the pitch will be unrivalled. The opportunity to play in a dominant team and deal with pressure. Because, OK, it might not be the Premier League up here, but in terms of pressure and resilience and mental fortitude, that's at the very highest level. If you can cope with that here, you can cope with it anywhere. But for any player coming, it's a wonderful opportunity to develop your game."

Ironically for someone like McCowan. Celtic is the end game. Who knows one day he could well become the Celtic captain and heir apparent to McGregor. What a thought that is. McCowan felt the full force of Celtic Park in all its splendour and glory last Sunday. He needn't have worried as the force was with him. It is largely why the opposition felt a great disturbance in the force. Callum McGregor is that force. He should be lauded and celebrated and his name shouted from the rooftops.

McGregor is a Captain. Leader. Legend. A force. He won't always be with you.